This is my brother. This is my sister.
Is this your sister? Yes, it is.
No, it isn't.
Who's this? This is my sister.
Who are these people? These are my cousins.
What's her name? Her name's Sue.
What's his name? His name's Ben.
What are their names? Their names are Sue and Ben.
When is your birthday? My birthday is in June.
When are your birthdays? Our birthdays are in May.
When are their birthdays? Their birthdays are in November.